High-density split-gate FinFET

ABSTRACT

Disclosed is a method and structure for forming a split-gate fin-type field effect transistor (FinFET). The invention produces a split-gate fin-type field effect transistor (FinFET) that has parallel fin structures. Each of the fin structures has a source region at one end, a drain region at the other end, and a channel region in the middle portion. Back gate conductors are positioned between channel regions of alternating pairs of the fin structures and front gate conductors are positioned between channel regions of opposite alternating pairs of the fin structures. Thus, the back gate conductors and the front gate conductors are alternatively interdigitated between channel regions of the fin structures.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention generally relates to transistors and moreparticularly to a fin-type field effect transistor (FinFET) that has afront gate and a back gate.

2. Description of the Related Art

The back-gated complementary metal oxide semiconductor (CMOS) is a knownmeans of achieving threshold voltage (Vt) control without the use ofdoping. Most structures that allow a back gate rely on burying a gateunder an silicon-on-insulator (SOI) silicon layer. As a result, thefront and back gates are very difficult to align to one another and tothe source drain edges. Furthermore, the gate dielectric for the backgate is very limited by processes that construct such a structure tohigh-temperature materials such as silicon dioxide. It is desirable forthe back gate to also be made of a low resistivity material such astungsten, which makes for fairly thick values of back gate dielectricfor good integrity electrically.

SUMMARY OF INVENTION

This invention introduces a structure of split gate FinFETs which allowfor dense connections for the two gates with an arbitrary numbers offins. This is done by burying a layer for interconnection of the “back”gate beneath an SOI layer and using sidewall image transfer (SIT) toprovide a self-aligned means of wiring the two gates in aninterdigitated fashion.

More specifically, the invention provides a method of forming asplit-gate fin-type field effect transistor (FinFET). The inventionstarts with a laminated structure (having a semiconductor layer) andpatterns parallel rectangular openings in the semiconductor layer. Thisforms the openings through an insulator layer below the semiconductorlayer to a back gate wiring layer below the insulator layer in thelaminated structure.

The invention forms back gate insulators on exposed portions of thesemiconductor layer within the openings, and then fills the openingswith a back gate conductor. Another insulator is formed above the backgate conductor. This insulator electrically separates the back gateconductors from the front gate conductor. The semiconductor layer ispatterned into fins, such that a fin is positioned adjacent each side ofthe back gate conductors. This patterning process leaves one side ofeach fin exposed (e.g., the side that is opposite the back gateconductor). Next, the invention forms front gate insulators on exposedportions of the fins and then deposits a front gate conductor(s) overthe exposed portions of the fins and the insulators. This leaves eachfin with a front gate on one side of the fin and a back gate on theother side of the fin.

The invention simultaneously patterns the back gate conductors and thefront gate conductor into linear gate conductors intersecting the fins.This process of patterning the back and front gate conductors isselective to the fins, such that ends of the fins are exposed after thepatterning process. This process of simultaneously patterning the backgate conductors and the front gate conductor automatically aligns theback gate conductors with the front gate conductor.

The invention then dopes the ends of the fins to form source and drainregions and forms conductive vias to the front gate conductor(s) (or toa front gate wiring layer) and to a back gate wiring layer (or to a wellregion electrically connected to the back gate conductors). Thelaminated structure comprises a silicon-on-insulator (SOI) and the backgate conductor controls the threshold voltage level of the FinFET.

Thus, the invention produces a split-gate fin-type field effecttransistor (FinFET) that has parallel fin structures. Each of the finstructures has a source region at one end, a drain region at the otherend, and a channel region in the middle portion. Back gate conductorsare positioned between channel regions of alternating pairs of the finstructures and front gate conductors are positioned between channelregions of opposite alternating pairs of the fin structures. Thus, theback gate conductors and the front gate conductors are alternativelyinterdigitated between channel regions of the fin structures. Also, eachof the channel regions has a back gate conductor on one side of each finstructure and a front gate conductor on the other side of the finstructure. The front gate conductors are positioned adjacent to outersides of channel regions of end fin structures of the split gate FinFET.There are also gate oxides between the back and front gate conductorsand the channel regions.

A back gate wiring layer, or well region, is positioned below the finstructures. The back gate wiring layer (or well region) is electricallyconnected to the back gate conductors. A front gate wiring layer can bepositioned above the fin structures. The front gate conductors and thefront gate wiring layer can comprise a continuous conductive unitarystructure. Such a front gate wiring layer is electrically connected tothe front gate conductors. A first conductive via is connected to theback gate wiring layer (or well region), and a second conductive via isconnected to the front gate wiring layer/front gate conductor(s). Afirst insulator layer is positioned between the back gate wiring layerand the front gate conductors and a second insulator layer is positionedbetween the front gate wiring layer and the back gate conductors.

The invention solves a number of problems associated with SOI structuresby providing a multiple-fin FinFET structure that has self-aligned frontand back gates. As mentioned previously, the channel regions in SOIstructures are placed above insulators and are therefore floating. Thus,it is important to provide a back gate in SOI structures in order tocontrol the voltage level of the channel region which provides thresholdvoltage of the transistor. The invention utilizes SOI fin channelregions that are electrically insulated above an insulating layer. Inorder to control the voltage of the fin channel regions, the back gateis placed on one side of the fin channel regions. The front gate ispositioned on the other side of the fin channel regions.

The front and back gates are patterned simultaneously (e.g., in the sameprocess using the same mask) which provides that the front and backgates will be naturally (automatically) aligned with each other. Thefront and back gates are also used to control the doping of thesource/drain regions 112 (wherein the channel region 114 is protected)which also allows the gates to be easily and accurately aligned with thesource/drain regions.

Thus, this method provides a structure that has front and back gatesthat are self-aligned with one another and with the source/drainregions. This allows the back gate to control the threshold voltage oftransistors even for structures that utilize multiple fins. With suchself-alignment, the power and delay is substantially decreased and thedensity of transistors is increased, leading to reduced costs.

These, and other, aspects and objects of the present invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following description, while indicatingpreferred embodiments of the present invention and numerous specificdetails thereof, is given by way of illustration and not of limitation.Many changes and modifications may be made within the scope of thepresent invention without departing from the spirit thereof, and theinvention includes all such modifications.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of a preferredembodiment(s) of the invention with reference to the drawings, in which:

FIG. 1 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 2 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 3 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 4 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 5 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 6 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 7 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 8 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 9 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 10 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 11 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 12 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 13 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 14 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 15 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 16 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 17 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 18 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 19 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 20 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 21 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 22 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 23 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 24 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 25 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 26 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 27 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 28 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 29 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention;

FIG. 30 is a cross-sectional schematic diagram of a partially completedFinFET structure according to the invention; and

FIG. 31 is a flow diagram illustrating a preferred method of theinvention.

DETAILED DESCRIPTION

The present invention and the various features and advantageous detailsthereof are explained more fully with reference to the nonlimitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. It should be noted that thefeatures illustrated in the drawings are not necessarily drawn to scale.Descriptions of well-known components and processing techniques areomitted so as to not unnecessarily obscure the present invention indetail.

FIG. 1 shows the SOI wafer prepared using known techniques (e.g., waferbonding) etc. To start with illustrated are a layer (beginning at thebottom) of substrate Si (10), a first buried oxide (12), buried bottomgate (polysilicon or silicide or tungsten or a combination thereof, 14),second buried oxide (16), active silicon (more generally, asemiconductor, 18), and pad films 20 (typically silicon nitride/oxidestack). FIG. 1 also shows the etch mask 22 on top of the entire stackthat is patterned 24.

FIG. 2 shows the openings 26 created by etching through the pad films20, active silicon 18, buried oxide 16, stopping on or within the buriedgate layer 14. FIG. 3 shows a gate oxidation 30 on the sidewalls of theactive silicon 18 and the gate layer 14; alternatively the gate oxidecan be any suitable gate insulator, such as hafnium silicate, orzirconium dioxide. FIG. 4 shows a spacer 40 of gate electrode material(polysilicon or tungsten, etc.) formed using conventional spacertechniques.

FIG. 5 shows a gate material 50 deposited, planarized and etched back torecess the electrodes below the top dielectric 22. A depositeddielectric 60 which is planarized and etched back below the topdielectric 22 is shown in FIG. 6. FIG. 7 shows the removal of the topdielectric 22 followed by formation of the spacer 70 on the resultantexposed fill dielectric 60. As shown in FIG. 8, the resultant structureafter the pad films 20 and active silicon 18 are etched with thedielectrics 60 and 70 used as a mask. A sacrificial oxidation, strip andgate oxide 80 formation follows. FIG. 9 shows the deposition of thesecond gate electrode material 90 followed by planarization andpatterning using mask 92.

As shown in FIGS. 10 and 11, respectively, the cross-sectional andtop-down views of photoresist patterning for the gate are followed byetching. The etch is selective to SiO₂ and etches the second gateelectrode material 90 and the first gate electrode material 50, as wellas the fill dielectric 60. Hence the first gate 50 edge is self-alignedto the second gate 90 edge because both are etched in the same processusing the same mask. FIG. 12 shows the patterned resist 120 and theetched gate electrodes, with the bottom oxide exposed where the gatematerial has been removed. In FIG. 13 the patterned resist in FIG. 12,120, is stripped, and a subsequent resist 121 is used to pattern bottomoxide 16, and bottom gate conductor 17. In FIG. 14 the resist 121, ofFIG. 13 is also stripped, followed by inter-layer dielectric (ILD)140deposition and planarization. FIG. 15 shows the complete structure withconductive vias 150, 152 to contact the first and second gates.

FIG. 16 illustrates a second embodiment that includes a conductive wellregion 164 within a silicon layer 160 that is used in place of thesubstrate 10, oxide 12, and bottom gate 14 in the laminate shown in FIG.1. The well 164 is formed by implanting impurities through the mask 162.Formation of the well region 164 is less expensive than forming theseparate wiring layer 14 that is discussed in the previous example.While this embodiment lowers the cost when compared to previousembodiment, it also increases resistance because the well region 164 hashigher resistance than the wiring layer 14. Thus, if the primary concernis cost, the well region 164 would be utilized however, if the primaryconcern is performance, the wiring layer 14 should be utilized. Theprocessing shown in the remaining drawings (FIGS. 17-31) is somewhatsimilar to the processing performed on the laminate shown in FIG. 1 andthe same numbers are reused in FIGS. 17-31 for the samestructures/processes.

More specifically, FIG. 17 shows the structure after removal of mask 162and formation and patterning of mask 22. FIG. 18 shows the openings 26created by etching through the pad films 20, active silicon 18, andburied oxide 16, stopping on or within the well region 164. FIG. 19shows a gate oxidation (or alternatively, deposition of a gatedielectric such as hafnium silicate, or zirconium dioxide) 30 on thesidewalls of the active silicon 18 and the well region 164. FIG. 20shows a spacer 40 of gate electrode material (polysilicon or tungsten,etc.) formed using conventional spacer techniques.

FIG. 21 shows a gate material 50 deposited, planarized and etched backto recess the electrodes below the top dielectric 22. A depositeddielectric 60 which is planarized and etched back below the topdielectric 22 is shown in FIG. 22. FIG. 23 shows the removal of the topdielectric 22 followed by formation of the spacer 70 on the resultantexposed fill dielectric 60. As shown in FIG. 24, the resultant structureafter the hardmask 20 and active silicon 18 are etched with the filldielectric 70 used as a mask. A sacrificial oxidation, strip and gateoxide (or alternatively, deposition of a gate dielectric such as hafniumsilicate, or zirconium dioxide) 80 formation follows. FIG. 25 shows thedeposition of the second gate electrode material 90 followed byplanarization. Patterning using mask 92 is shown in FIG. 26.

As shown in FIGS. 26 and 27, respectively, the cross-sectional andtop-down views of photoresist patterning for the gate are followed byetching. The etch is selective to SiO2 and etches the second gateelectrode material 90 and the first gate electrode material 50, as wellas the fill dielectric 60. Hence the first gate 50 edge is self-alignedto the second gate 90 edge because both are etched in the same processusing the same mask. FIG. 28 shows the patterned resist 120 and etch ofthe top buried oxide (BOX) 16 as well as the exposed first gateelectrode 50. FIG. 29 shows the resist 120 from FIGS. 28 and 29stripped, followed by inter-layer dielectric (ILD)140 deposition andplanarization. FIG. 30 shows the complete structure with conductive vias150, 152 to contact the first gate and well region 164.

FIG. 31 is a flowchart representation of the invention and begins withitem 300, where the laminated structure (either FIG. 1 or 17) isprovided/formed. Next, as shown in item 302, parallel rectangularopenings 26 are formed in the semiconductor layer 18. This forms theopenings 26 through the insulator layer 16 below the semiconductor layer18 to either the back gate wiring layer 14 or the well region 164 belowthe insulator layer 18 in the laminated structure.

In item 304, the invention forms back gate insulators 30 on exposedportions of the semiconductor layer 18 within the openings 26, and thenfills the openings 26 with a back gate conductor 50 (item 306). Anotherinsulator 60 is formed above the back gate conductor 50 in item 308.This insulator 60 electrically separates the back gate conductors 50from the front gate conductor 90 that is formed later. In item 310, thesemiconductor layer 18 is patterned into fins by operation of thesidewall spacer masks 70 that are adjacent the insulators 60. After thisprocessing, a fin 18 is positioned adjacent each side of the back gateconductors 50, as shown in FIGS. 8 and 24. This patterning processleaves one side of each fin 18 exposed (e.g., the side that is oppositethe back gate conductor 50). Next, in item 312, the invention formsfront gate insulators 80 on exposed portions of the fin 18 s and then(in item 314) deposits a front gate conductor(s) 90 over the exposedportions of the fins 18 and the insulators 60, 70, 80. This leaves eachfin 18 with a front gate conductor 90 on one side of the fin 18 and aback gate conductor 50 on the other side of the fin 18.

The invention simultaneously patterns the back gate conductors 50 andthe front gate conductor 90 into linear gate conductors 110 intersectingthe fins 18 in item 316 as shown in the top-view diagrams in FIGS. 11and 27. This process 316 of patterning the back and front gateconductors 50, 90 is selective to the fins 18, such that ends 112 of thefins 18 are exposed after the patterning process. This process ofsimultaneously patterning the back gate conductors 50 and the front gateconductor 90 automatically aligns the back gate conductors 50 with thefront gate conductor 90.

In item 318, the invention then dopes the ends 112 of the fins 18 toform source and drain regions and (in item 320) forms conductive vias tothe front gate conductor(s) (or to a front gate wiring layer) 90 and toa back gate wiring layer 14 (or to a well region 164 electricallyconnected to the back gate conductors 50). The laminated structurecomprises a silicon-on-insulator (SOI) structure and the body voltagelevel floats because the transistors are insulated by the underlyinginsulating layer 16. The back gate conductor 50 controls the thresholdvoltage level of the FinFET by modulating the potential of the channeladjacent to the front gate.

Thus, the invention produces a split-gate fin-type field effecttransistor (FinFET) that has parallel fin 18 structures. Each of the finstructures 18 has a source region at one end 112, a drain region at theother end 112, and a channel region 114 in the middle portion. Back gateconductors 50 are positioned between channel regions 114 of alternatingpairs of the fin structures 18 and front gate conductors 90 arepositioned between channel regions 114 of opposite alternating pairs ofthe fin structures 18. Thus, the back gate conductors 50 and the frontgate conductors 90 are alternatively interdigitated between channelregions of the fin structures 18. Also, each of the channel regions hasa back gate conductor 50 on one side of each fin structure 18 and afront gate conductor 90 on the other side of the fin structure 18. Thefront gate conductors 90 are positioned adjacent to outer sides ofchannel regions of end fin structures 18 of the split gate FinFET. Thereare also gate oxides 30, 80 between the back and front gate conductors90 and the channel regions 114.

A back gate wiring layer 14 or well region 164, is positioned below thefin structures 18. The back gate wiring layer 14 (or well region 164) iselectrically connected to the back gate conductor 50. A front gatewiring layer 90 can be positioned above the fin structures 18. The frontgate conductors and the front gate wiring layer can comprise acontinuous conductive unitary structure 90. Such a front gate wiringlayer is electrically connected to, or part of, the front gateconductors. A first conductive via 152 is connected to the back gatewiring layer 14 (or well region 164), and a second conductive via 150 isconnected to the front gate wiring layer/front gate conductor(s) 90. Afirst insulator layer 16 is positioned between the back gate wiringlayer 14 and the front gate conductors 90 and a second insulator layer60, 70 is positioned between the front gate wiring layer 90 and the backgate conductors 50.

Thus, the invention solves a number of problems associated withback-gate-SOI structures by providing a FinFET structure that hasself-aligned front and back gates. As mentioned previously, the channelregions in SOI structures are placed above insulators and are thereforefloating. Thus, it is important to provide a back gate in SOI structuresin order to control the voltage level of the channel region whichprovides threshold voltage of the transistor. As shown most clearly inFIGS. 15 and 31, the invention utilizes SOI fin channel regions 18 thatare electrically insulated above insulating layer 16. In order tocontrol the threshold voltage of the fin channel regions 18, the backgate 50 is placed on one side of the fin channel region 18. The frontgate 90 is positioned on the other side of the fin channel region 18.

In FIGS. 11 and 27 (which are top-view of the structures) the front gate90 and back gate 50 are represented by a single item 110 because theback gate 50 lies directly below the front gate 90. Further, asdescribed above, the front and back gates 110 are patternedsimultaneously (e.g., in the same process using the same mask) whichprovides that the front and back gates will be naturally (automatically)aligned with each other. Note that the front gate and back gate 110 arealso used to control the doping of the source/drain regions 112 (whereinthe channel region 114 is protected) which allows the gates to be easilyand accurately aligned with the source/drain regions.

Thus, this method provides a structure that has front and back gatesthat are self-aligned with one another and with the source/drainregions. This allows the back gate to control the threshold voltage oftransistors even for structures that utilize multiple fins. With suchself-alignment, the gate, source, and drain capacitances are allreduced, resulting in reduced power dissipation and reduced circuitdelay. The size of the transistor is also reduced, resulting inincreased circuit density and decreased manufacturing costs. Low powerapplications such as cell phones, PDAs, and other mobile products can befabricated with higher performance and longer battery lifetimes when theinvention is utilized.

While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

1. A split-gate fin-type field effect transistor (FinFET) comprising: aplurality of parallel fin structures; back gate conductors adjacent saidfin structures; and front gate conductors adjacent said fin structures,wherein said back gate conductors and said front gate conductors arealternatively interdigitated between channel regions of said finstructures such that each of said channel regions has a back gateconductor on one side of each fin structure and a front gate conductoron the other side of said fin structure.
 2. A split-gate fin-type fieldeffect transistor (FinFET) comprising: a plurality of parallel finstructures; back gate conductors between channel regions of alternatingpairs of said fin structures; front gate conductors between channelregions of opposite alternating pairs of said fin structures; a backgate wiring layer connected to said back gate conductors; a front gatewiring layer connected to said front gate conductors; a first insulatorlayer positioned between said front gate conductors and said back gatewiring layer; and a second insulator layer positioned between said backgate conductors and said front gate wiring layer.
 3. The split-gateFinFET in claim 2, further comprising: a first conductive via connectedto said back gate wiring layer; and a second conductive via connected tosaid front gate wiring layer.
 4. The split-gate FinFET in claim 2,wherein said front gate conductors and said front gate wiring layercomprise a continuous conductive unitary structure.
 5. The split-gateFinFET in claim 1, wherein ones of said front gate conductors arepositioned adjacent to outer sides of channel regions of end finstructures of said split gate FinFET.
 6. The split-gate FinFET in claim1, further comprising gate insulators between said back and font gateconductors and said channel regions.
 7. The split-gate FinFET in claim1, wherein said back gate controls the threshold voltage level of saidsplit-gate FinFET.
 8. A split-gate fin-type field effect transistor(FinFET) comprising: a plurality of parallel fin structures, whereineach of said fin structures comprises a source region in a first end ofsaid fin, a drain region in a second end of said fin, and a channelregion in a middle portion of said fin between said first end and saidsecond end; back gate conductors between channel regions of alternatingpairs of said fin structures; front gate conductors between channelregions of opposite alternating pairs of said fin structures, such thatsaid back gate conductors and said front gate conductors arealternatively interdigitated between channel regions of said finstructures and such that each of said channel regions has a back gateconductor on one side of each fin structure and a front gate conductoron the other side of said fin structure; a well region positioned belowsaid fin structures, wherein said well region is electrically connectedto said back gate conductors; and a front gate wiring layer positionedabove said fin structures, wherein said front gate wiring layer iselectrically connected to said front gate conductors.
 9. The split-gateFinFET in claim 8, further comprising: a first insulator layerpositioned between said well region and said front gate conductors; anda second insulator layer positioned between said front gate wiring layerand said back gate conductors.
 10. The split-gate FinFET in claim 8,further comprising: a first conductive via connected to said wellregion; and a second conductive via connected to said front gate wiringlayer.
 11. The split-gate FinFET in claim 8, wherein said front gateconductors and said front gate wiring layer comprise a continuousconductive unitary structure.
 12. The split-gate FinFET in claim 8,wherein ones of said front gate conductors are positioned adjacent toouter sides of channel regions of end fin stabs of said split gateFinFET.
 13. The split-gate FinFET in claim 8, further comprising gateoxides between said back and front gate conductors and said channelregions.
 14. The split-gate FinFET in claim 8, wherein said back gatecontrols the threshold voltage level of said split-gate FinFET.
 15. Asplit-gate fin-type field effect transistor (FinFET) comprising: aplurality of parallel fin structures, wherein each of said finstructures comprises a source region in a first end of said fin, a drainregion in a second end of said fin, and a channel region in a middleportion of said fin between said first end and said second end; backgate conductors between channel regions of alternating pairs of said finstructures; front gate conductors between channel regions of oppositealternating pairs of said fin structures, such that said back gateconductors and said front gate conductors are alternativelyinterdigitated between channel regions of said fin structures and suchthat each of said channel regions has a back gate conductor on one sideof each fin structure and a front gate conductor on the other side ofsaid fin structure; a back gate wiring layer positioned below said finstructures wherein said back gate wiring layer is electrically connectedto said back gate conductors; and a front gate wiring layer positionedabove said fin structures, wherein said front gate wiring layer iselectrically connected to said front gate conductors.
 16. The split-gateFinFET in claim 15, further comprising: a first insulator layerpositioned between said back gate wiring layer and said front gateconductors; and a second insulator layer positioned between said frontgate wiring layer and said back gate conductors.
 17. The split-gateFinFET in claim 15, comprising: a first conductive via connected to saidback gate wiring layer; and a second conductive via connected to saidfront gate wiring layer.
 18. The split-gate FinFET in claim 15, whereinsaid front gate conductors and said front gate wiring layer comprise acontinuous conductive unitary structure.
 19. The split-gate FinFET inclaim 15, wherein ones of said front gate conductors are positionedadjacent to outer sides of channel regions of end fin structures of saidsplit gate FinFET.
 20. The split-gate FinFET in claim 15, furthercomprising gate insulators between said back and front gate conductorsand said channel regions.
 21. The split-gate FinFET in claim 15, whereinsaid back gate controls the threshold voltage level of said split-gateFinFET.